High-pressure discharge lamp

ABSTRACT

A high-pressure discharge lamp has a lead-through through the wall of the discharge space of the lamp which has a relatively high electrical resistance. In the operating condition of the lamp, heat is therefore evolved in this lead-through by the lamp current. As a result an end of the discharge vessel which generally includes the lead-through can be maintained at the desired relarively high temperature in a simple manner, which enhances the value of the luminous flux of the lamp.

United States Patent Schat et al.

HIGH-PRESSURE DISCHARGE LAMP Inventors: Bralt Renze Schat; Abraham Timmermans, both of Emmasingel, Eindhoven, Netherlands Assignee: U.S. Philips Corporation, New

York, NY.

Filed: Feb. 13, 1973 Appl. No.: 332,117

Foreign Application Priority Data Feb. 21, 1972 Netherlands 7202269 US. Cl. 313/220; 313/221; 313/318; 313/332; 315/49; 315/50; 315/71 Int. Cl H01j61/30; HOlj 61/82 Field of Search 313/220, 221, 318, 331, 313/332; 315/49, 50, 71

References Cited UNITED STATES PATENTS 3/1959 Schlosser et al. 315/49 51 May 20, 1975 3,742,283 6/1973 Loughridge .1 313/318 FOREIGN PATENTS OR APPLICATIONS 1,074,124 6/1967 United Kingdom Primary Examiner-Ronald L. Wibert Assistant Examiner-Richard A. Rosenberger 5 7 ABSTRACT A high-pressure discharge lamp has a lead-through through the wall of the discharge space of the lamp which has a relatively high electrical resistance. In the operating condition of the lamp, heat is therefore evolved in this lead-through by the lamp current. As a result an end of the discharge vessel which generally includes the lead-through can be maintained at the desired relatively high temperature in a simple manner, which enhances the value of the luminous flux of the lamp.

8 Claims, 1 Drawing Figure HIGH-PRESSURE DISCHARGE LAMP The invention relates to a high-pressure discharge lamp provided with a discharge tube which includes at least one internal electrode and a current lead-through conductor connected to said electrode.

A high-pressure discharge lamp of the kind referred to is described, for example. in French Pat. No. 1,557,527.

A drawback of this known discharge lamp is that the ends of the discharge tube in the operating condition often assume too low temperature. This causes too small a vapour pressure in the discharge tube and this in turn leads to a relatively low efficiency, for example, expressed in lumens/watt.

Steps were proposed to being these ends of the discharge tube to a higher temperature. But these were steps necessitating extra components such as strips provided about the ends of the discharge tube. Furthermore this had the drawback that several stages had to be added to the manufacture of the lamp.

An object of the invention is to provide a highpressure discharge lamp of the kind described in the preamble in which in the operating condition a discharge tube end acquires a sufficiently high temperature and in which this is realized in a simple manner without the complication of strips about such an end.

According to the invention a high-pressure discharge lamp provided with a discharge tube which includes at least one internal electrode and a current lead-through conductor connected to said electrode is characterized in that the resistance of the path of the current leadthrough conductor between the outer wall and the inner wall of the discharge tube is so large that in the operating condition of the lamp the product of this re sistance (in ohms) and the current (in amperes) through this lead-through conductor is more than l.O-.

An advantage of this lamp is that the heat evolved by the electrical current in the lead-through path referred to can bring the relevant place to a slightly higher temperature so that the drawback of the too cold ends of the discharge tube occurring in the said known lamp can be avoided. As will be evident the voltage drop across the path of the current leadthrough conductor in a lamp according to the invention is at least [.0- Volt.

The relatively high voltage drop across the leadthrough path can be realized, for example, by giving the lead-through conductor a slight cross-section at its leadthrough area. The lead-through may consist of a rod or a tube or of a collection of parallel-arranged conductors. In the latter case the joint cross-section of these conductors is of course to be taken into account. It is to be noticed that the coefficient of expansion of the material of the lead-through conductor is in satisfactory conformity with the coefficient of expansion of the material through which the lead-through conductor protrudes. When closing a discharge tube by means of a closing member consisting for the greater part of aluminum oxide, the material of the lead-through conductor through this member may consist of, for example, niobium. As is known the coefficients of expansion of aluminum oxide and niobium correspond satisfactorily.

A high-pressure discharge lamp according to the invention is preferably formed in such a manner that the current lead-through conductor is also the closing member for the dischage tube.

An advantage of this preferred embodiment is that the current lead-through conductor then has a triple function, for it serves for the current supply of the electrode in the discharge tube, furthermore for the evolution of heat at an end of the discharge tube and finally as a closing member for the discharge tube.

It is to be noted that the combination of the current lead-through feature and the closing feature in itself is known, for example, from United Kingdom Specifications No. 961,070 and l,074,234. The resistance of the lead-through path was, however, very low. In the case of the United Kingdom Patent No. l,074,l24 a separated heating wire was therefore used for obtaining hot ends of the discharge tube.

The coefficient of expansion of the material for the closing member in high-pressure discharge lamps according to the invention preferably differs not more than 3Xl0 "'/C from the coefficient of expansion of the material for the wall of the discharge tube.

An advantage thereof is that the connection between the closing member and the wall of the discharge vessel may be relatively simple.

When in a high-pressure discharge lamp according to the invention the wall of the discharge tube mainly consists of a ceramic material, particularly aluminum oxide, the path of the current lead-through conductor is preferably a cermet, particularly an aluminum-oxide cermet, whose ceramic constituent has the same composition as the ceramic material for the wall of the discharge tube.

Cermet is understood to mean a refractory material consisting of a heterogeneous combination of one or more metals and/or alloys having one or more ceramic phases.

An advantage of this embodiment is that for highpressure discharge lamps such as, for example, highpressure sodium vapour discharge lamps or highpressure discharge lamps using mercury and one or more halides in the discharge tube a sealing of the discharge tube can be obtained which is reliable due to the satisfactory conformity between the coefficients of expansion of the parts constituting the discharge tube, which is an additional advantage to the advantage of the simple current lead-through and of sufficiently hot discharge tube ends.

In the latter preferred embodiment, in the case of using an aluminum oxide cermet, this cermet also includes a metal selected from the group consisting of iron and molybdenum and a connecting conductor of the cermet includes this same metal.

An advantage of this preferred embodiment is that the adhesion of this connecting conductor to the cermet, if this connecting conductor is (partly) inserted into the cermet. is satisfactory because an intimate contact is possible between the metal of the connecting conductor and the metal phase of the cermet.

In a last preferred embodiment ofa high-pressure discharge lamp according to the invention the discharge tube not only includes the first internal electrode but also a second internal electrode and the second internal electrode is connected to a second current leadthrough conductor whose resistance of the path between the outer wall and the inner wall of the discharge tube is so large that in the operating condition of the lamp the product of this resistance (in ohms) and the current (in amperes) through this second current leadthrough conductor is more than 1.0-.

An advantage of this lamp is that none of the two ends can become too cold This lamp can therefore be used. for example, in more operating positions than a lamp whose discharge tube has only one tube end which can be maintained at a sufficiently high temperature.

The invention will be described in detail with reference to the drawing.

The drawing shows a longitudinal section of a highpressure discharge lamp according to the invention The lamp shown is a high-pressure sodium vapour discharge lamp of 400 Watts. 1 denotes a discharge tube. This tube is surrounded by an outer envelope 2. 3 denotes a lamp cap.

The discharge tube 1 has a cylindrical wall (4) consisting of densely sintered (polycrystalline) aluminum oxide. This wall may alternatively consist of, for example, sapphire. The tube 1 is sealed by means of two eylindrical studs 5 and 6 of an aluminum oxide cermet In the relevant ease this was a molybdenum/aluminum oxide cermet. The studs 5 and 6 are secured to the ends of the tube wall 4 by means of melting glass A molybdenum rod 7 leading to an internal electrode 8 is secured in the stud 5. 9 denotes a molybdenum current supply rod. In a similar manner stud 6 is provided with molybdenum rods 10 and 12, rod 10 leading to a sccond internal electrode (1]). l3 denotes a terminal wire which is connected to the rod 9.

The operating voltage of the lamp shown was approx imately lOS Volts and the lamp current was approximately 44 amperes. The cermet studs 5 and 6 had a re' sistance between the rods 9 and 7 and between the rods 12 and 10 of approximately 0.4 Ohm. The voltage drop across each of these studs was consequently approximately 4.4 X 0.4 1.76 Volts. Thus, this was more than the said value of 1.0-Volt.

Each of the cermet studs 5 and 6 had a diameter of approximately 10 mms and a thickness between the rods of approximately I mm. The specific resistivity, p (rho). of this cermet was approximately 0.4 Ohm.cm. The volume ratio between molybdenum and aluminum oxide was approximately 1 80. The difference in coefficient of expansion relative to that of wall 4 was less than 3.l0 Ct In the lamp described the evolved heat in each of the studs 5 and 6 was approximately 7.5 Joule/second. This was sufficient to maintain these ends of the tube 1 at a temperatureof approximately ],U50 Kelvin.

In a lamp not according to the invention in which the closures of the discharge tube has a much lower resistance, complicated strips around the ends of the discharge tube 1 were required so as to obtain the same lumen value (approximately 47.000 lumen).

What is claimed is:

l. A high-pressure discharge lamp for use with an aslead-through conductor connected to said electrode the electrical resistance of the path of the current through said lead-through conductor between the outer wall and the inner wall of the discharge tube being so large that in the operating condition of the lamp. the product of said resistance (in ohms) and the current (in ampcres) through said lead-through conductor is more than [0.

2. A high-pressure discharge lamp as claimed in claim 1, in which the discharge tube not only includes the first internal electrode but also a second internal electrode, and wherein the second internal electrode is connected to a second current lead'through conductor whose resistance of the path between the outer wall and the inner wall of the discharge tube is so large that in the operating condition of the lamp the product of said resistance (in ohms) and the current (in amperes) through said second current lead-through conductor is more than 1.0.

3. In a high-pressure discharge lamp comprising a discharge tube which includes at least one internal electrode and a current lead-through conductor connected to said electrode, the electrical l'CSlSlill'll c of the path of the current through said lead-through conductor between the outer wall and the inner wall of the discharge tube being so large that in the operating condition of the lamp, the product of said resistance (in ohms) and the current (in amperes) through said lead'through conductor is more than 1.0 said current lead-through conductor being also the closing member for the discharge tube.

4. A high-pressure discharge lamp as claimed in claim 3, wherein the coefficient of expansion of the material for the closing member differs not more than 3X l0 /C from the coefficient of expansion of the material for the wall of the discharge tube.

5. A high-pressure discharge lamp as claimed in claim 4, in which the wall of the discharge tube is a ceramic material, wherein the current lead-through consists of a cermet whose ceramic constituents has the same composition as the ceramic material of the wall of the discharge tube.

6. A highpressure discharge lamp as claimed in claim 5, in which the wall of the discharge tube mainly consists of aluminum oxide wherein the current leadthrough conductor consists of an aluminum oxide cermet.

7. A high-pressure discharge lamp as claimed in claim 6, wherein the aluminum oxide cermet includes iron and a connecting conductor of the aluminum oxide cermet consists of iron.

8. A high-pressure discharge lamp as claimed in claim 6, wherein the aluminum-oxide cermet includes molybdenum and a connecting conductor of the aluminumoxide cermet consists of molybdenum. 

1. A high-pressure discharge lamp for use with an associated ballast comprising a discharge tube which includes at least one internal electrode and a current lead-through conductor connected to said electrode, the electrical resistance of the path of the current through said lead-through conductor between the outer wall and the inner wall of the discharge tube being so large that in the operating condition of the lamp, the product of said resistance (in ohms) and the current (in amperes) through said lead-through conductor is more than 1.0.
 2. A high-pressure discharge lamp as claimed in claim 1, in which the discharge tube not only includes the first internal electrode but also a second internal electrode, and wherein the second internal electrode is connected to a second current lead-through conductor whose resistance of the path between the outer wall and the inner wall of the discharge tube is so large that in the operating condition of the lamp the product of said resistance (in ohms) and the current (in amperes) through said second current lead-through conductor is more than 1.0.
 3. In a high-pressure discharge lamp comprising a discharge tube which includes at least one internal electrode and a current lead-through conductor connected to said electrode, thE electrical resistance of the path of the current through said lead-through conductor between the outer wall and the inner wall of the discharge tube being so large that in the operating condition of the lamp, the product of said resistance (in ohms) and the current (in amperes) through said lead-through conductor is more than 1.0 said current lead-through conductor being also the closing member for the discharge tube.
 4. A high-pressure discharge lamp as claimed in claim 3, wherein the coefficient of expansion of the material for the closing member differs not more than 3 X 10 6/*C from the coefficient of expansion of the material for the wall of the discharge tube.
 5. A high-pressure discharge lamp as claimed in claim 4, in which the wall of the discharge tube is a ceramic material, wherein the current lead-through consists of a cermet whose ceramic constituents has the same composition as the ceramic material of the wall of the discharge tube.
 6. A high-pressure discharge lamp as claimed in claim 5, in which the wall of the discharge tube mainly consists of aluminum oxide wherein the current lead-through conductor consists of an aluminum oxide cermet.
 7. A high-pressure discharge lamp as claimed in claim 6, wherein the aluminum oxide cermet includes iron and a connecting conductor of the aluminum oxide cermet consists of iron.
 8. A high-pressure discharge lamp as claimed in claim 6, wherein the aluminum-oxide cermet includes molybdenum and a connecting conductor of the aluminum-oxide cermet consists of molybdenum. 